Some persons suffer from acute respiratory failure, for example consecutive to pneumonia, pulmonary edema or superinfection of chronic respiratory diseases. Mechanical ventilatory support may prove to be necessary for these persons. Ventilatory support machines or ventilators include means for detecting inspiration by the patient and means for assisting the patient with inspiration by increasing the flow or pressure of the air collected by the patient. The ventilators also include means for detecting expiration and means for interrupting the inspiratory activity of the ventilator when expiration is detected, which allows synchronizing at best the activity of the patient and that of the ventilator.
Thus, the support consists in providing a predetermined volume of gas or in pressurization of the airways. In both cases, various settings allow the gas flow to be adapted to the needs of the patient. The support machine has to be adapted to the ventilatory behavior of the patients so that the relationship which binds them is “harmonious”, i.e. the patient is in a satisfactory physical comfort condition, in which the patient does not feel any difficulty in breathing during ventilatory support. With inadequate adjustments, for example when the provided airflow is too high or, on the contrary, too low, the patient may be in an uncomfortable situation, or even be in a respiratory distress situation. The same applies when the inspiratory activity of the ventilator continues while the patient is in an expiration phase. It seems that such circumstances are deleterious for the patient.
In order to detect such a disharmony between the patient and the ventilator, resulting from improper adjustment of the ventilator, different means have been used. In particular, it is possible to simply question the patient. However, this is not possible when the patient is asleep or in a coma.
It is also possible to observe the ventilatory activity of the patient, and notably the frequency and the use of the different respiratory muscle groups.
Finally, it is possible to study pressure and flow rate signals provided by the ventilator for detecting the occurrence of events showing imperfect synchronization of the ventilator and of the patient. There exist various profiles showing this imperfect synchronization, such as for example “ineffective appeals”, during which the patient makes an inspiratory effort which is not “rewarded” by the ventilator.
In practice, these means prove to be delicate to use and are all indirect witnesses of the sensations which the patient may feel.
French Patent Publication No. 2 903 314 (“FR '314”) describes a method for detecting a disharmony between a patient and a ventilator consisting, for each breathing cycle, of measuring an electroencephalographic signal over a measurement interval extending around a respiratory initiation time, and of then averaging the electroencephalographic signals measured over several measurement intervals and finally processing the thereby obtained averaged signal in order to infer therefrom possible disharmony between the patient and the ventilator.
Such a method does not give entire satisfaction. Indeed, in situations of discomfort or respiratory distress resulting from disharmony between the patient and the ventilator, it is important to be able to detect this disharmony and to find a remedy thereto as rapidly as possible for restoring harmony between the patient and his/her ventilator.
The method as described in FR '314, requires measurement and averaging of an electroencephalographic signal over at least sixty to eighty breathing cycles so as to be able to conclude that disharmony exists. This on average corresponds to a duration of four to five minutes, during which the detected disharmony is by definition not subject to a correction, whether this correction is carried out by a physician alerted by the identification of the abnormal electroencephalographic signal, or by the activation of a control loop on the ventilator. Moreover, the signal measured by the averaging process, called a pre-motor potential, may easily be subject to interferences, either due to the movements of the patient or due to the electromagnetic pollution characteristic of resuscitation and intensive care environments. Thus, it appears to be desirable to improve both the reactivity and the reliability of electroencephalographic detection of patient-ventilator disharmony.
An object of the invention is therefore to provide a system for electroencephalographic detection of an improper adjustment of a ventilator which is more reliable, and in particular which allows detection in real time of disharmony and therefore of an improper adjustment of a ventilator.